1. Field of the Invention
The present invention relates generally to insertion and extraction of prosthetic acetabular components and, more particularly, to prosthetic acetabular components, to insertion and extraction tools for releasable locking engagement with prosthetic acetabular components and to methods of locking prosthetic acetabular components to insertion and extraction tools.
2. Brief Discussion of the Related Art
Many surgical procedures involve the implantation of prosthetic components on prepared bone surfaces, particularly the bone surfaces of anatomical joints. In the area of hip surgery, prosthetic acetabular components are commonly implanted on prepared bone surfaces of the acetabulum to provide a socket for articular engagement with a head at the upper end of the femur. Prosthetic acetabular components typically have a partial spherical configuration, and preparation of the acetabulum to receive an acetabular component generally involves the formation of a cavity in the bone to receive the partial spherical configuration. Ordinarily, it is desirable that the cavity in the bone be no larger than necessary to accommodate the acetabular component so as to preserve as much natural bone as possible. It is also desirable that the thickness of the partial spherical wall of the acetabular component be no thicker than necessary in order to minimize the size of the cavity required to be formed in the bone for a given size articular surface area.
Insertion of prosthetic acetabular components in the prepared bone cavities often necessitates the application of significant impaction forces on the acetabular components, especially where the components are designed to be jam or interference fitted in the bone cavities. Prior to fixation of the acetabular components in the bone cavities, the position of the acetabular components in the cavities may have to be adjusted in order to establish optimal fit and orientation of the acetabular components with the head at the upper end of the femur. Adjustment may involve moving the acetabular components relative to the bone cavities until correct positioning is achieved. In order to enhance the efficiency of the surgical procedures, it is desirable for adjustment to be effected while the acetabular components remain within or close to the bone cavities without having to be withdrawn from the patients' bodies. Extraction of acetabular components from the bone cavities after being fixated to the bone typically requires that vigorous extraction forces be applied to the acetabular components since the extraction forces must be strong enough to overcome the fixation by which the acetabular components are fixated in the bone cavities.
Various tools have been proposed for mechanically engaging acetabular components for insertion in and/or extraction from bone cavities as represented by U.S. Pat. No. 5,037,424 to Aboczsky, U.S. Pat. No. 5,169,399 to Ryland et al, U.S. Pat. No. 5,250,051 to Maryan, U.S. Pat. No. 5,417,696 to Kashuba et al, U.S. Pat. No. 5,486,181 to Cohen et al, U.S. Pat. No. 5,540,697 to Rehmann et al, U.S. Pat. No. 5,658,294 to Sederholm, U.S. Pat. No. 5,683,399 to Jones, U.S. Pat. No. 5,904,688 to Gilbert et al and U.S. Pat. No. 6,063,124 to Amstutz, and by U.S. patent application Publication No. 2002/0177854 A1 to Tuke et al. Prior tools are not self-locking with the acetabular components and require complicated structure and operating steps in order to effect locking of the acetabular components to the tools. The mechanical lock between the acetabular components and prior tools may not be strong enough for the applied impaction and/or extraction forces so that damage may occur to the acetabular components and/or the tools. Prior tools may become loose from the acetabular components as a result of vibration and/or twisting. Where permanent locking structure is provided on the inner surfaces of the acetabular components, the locking structure may interfere with or detract from the articular surface. Moreover, locking structure on the inner surfaces may detrimentally interfere with the femoral head in articular engagement with the socket of the acetabular component.
The Gilbert et al patent discloses an insertion tool including a body having a plurality of L-shaped fingers for being introduced in corresponding notches in a thick-walled acetabular cup and then rotated to engage undercut walls of the notches. A projection is thereafter insertable into the portion of only one of the notches which is unoccupied by the corresponding finger to prevent rotation of the body relative to the acetabular cup. In order to insert the projection in and withdraw the projection from the unoccupied portion of the notch, a finger grip that is separate from the handle of the tool must be manually moved axially and rotatably to effect extension and retraction of the projection. Accordingly, the tool is not self-locking with the acetabular cup but, rather, requires a series of complicated manipulations to effect locking and unlocking. The finger grip is inconveniently located remote from the gripping knob of the handle, thusly requiring two-handed operation. Only one projection and finger grip are provided, such that the weight of the locking structure and finger grip are not distributed evenly about the longitudinal axis of the tool. The resulting weight imbalance impairs the surgeon's ability to manipulate the tool with ease and accuracy via the handle. The tool does not have a centering device to facilitate axial alignment of the tool with the acetabular cup when introducing the fingers in the notches.
The Tuke et al patent relates to an impactor having a cable threaded through a corresponding acetabular cup and/or a removable cover for the acetabular cup, with the cable being looped over arms or mooring pegs of the impactor. Regardless of whether the cable is threaded prior to or during surgery, the threading procedure is tedious and labor intensive. It is possible for the cable to become caught on anatomical structure or other instruments at the surgical site, thereby complicating the surgical procedure. In order to effect locking of the acetabular cup to the impactor via the cable, the cable is tensioned by advancing a carriage of the impactor via manual rotation of a knob. Significant mechanical effort is needed to obtain minimal advancement of the carriage and adds to the time required to complete the surgical procedure. Once the impactor is disconnected from the acetabular cup following implantation, the cable must be cut and removed from the patient's body. The patient is therefore placed at risk since the cable could be accidentally dropped inside the patient's body and/or left in the patient's body inadvertently. Extraction using the tool is not feasible.
The acetabular cup disclosed in the Amstutz patent has recesses within its peripheral rim for engagement with fingers of a bayonet coupler of an impactor and/or extractor tool. The acetabular cup must be moved away from the bayonet coupler by a securing member of the tool in order to lock the fingers in the recesses. The recesses are enclosed between the inner and outer surfaces of the partial spherical wall of the acetabular cup, thereby requiring a thicker wall and a larger size cavity in the acetabulum.